Energy reclaiming multizone air processing system

ABSTRACT

An air processing system for an enclosure having at least two temperature zones. The system includes a multizone heating, ventilating and air conditioning unit and a control mechanism which continuously monitors the energy utilized by the hot deck energy source and the enthalpy of the outdoor air drawn into the system to determine and effect the most efficient operation of the multizone unit.

O Umted States Patent 1191 1 1 3, Gilles 5] Dec. 23, 1975 ENERGY RECLAIMING MULTIZONE AIR 3,820,713 6/1974 Demaray 165/22 x PROCESSING SYSTEM 3,841,393 10/1974 Gilles 165/22 75 I t nven or ilgllvegdore C Gilles, Marshalltown, Primary Examiner Albert W. Davis, Jr.

Assistant Examiner--Sheldon Richter [73] Assignee: Lennox Industries Inc., Attorney, Agent, or Firm-M0linare, Allegretti, Newitt Marshalltown, Iowa & Witcoff [22] Filed: Oct. 4, 1974 21 App]. No.2 512,100 [57] ABSTRACT An air processing system for an enclosure having at least two temperature zones. The system includes a 165/ multizone heating, ventilating and air conditioning [58] Fieid 236/91 D unit and a control mechanism which continuously monitors the energy utilized by the hot deck energy source and the enthalpy of the outdoor air drawn into [56] References Cited the system to determine and effect the most efficient UNITED STATES PATENTS operation of the multizone unit. 3,567,115 12/1970 Nelson 165/22 X 3,788,386 1/1974 Demaray 165/22 x 10 Clams 5 Drawmg Flgm'es 1 I 48 a 88 46 EMS-$1 72 p 40 1 1 l j 1 I I: 26 x im 44 i T 115 1 U.S. Patent Dec. 23, 1975 Sheet 1 of3 3,927,713

DRY BULB 55 ENERGY RECLAIMING MULTIZONE AIR PROCESSING SYSTEM BACKGROUND OF THE INVENTION tion of the multizone unit depends upon temperature 1 and energy considerations.

The temperatures and thermal loads within a multizone enclosure or facility vary continuously. The factors determining the supply air temperature requirements of the various temperature zones within the enclosure include, among others, solar effect, occupancy and lighting variations, and ambient conditions, such as wind, etc.

Two basic systems have been utilized to meet these diverse heating and cooling requirements of a multizone enclosure. One utilizes multiple single zone heat- .ing and cooling units. As implied, each separate zone is served by a heating and cooling unit.

The other basic system utilizes a multizone heating, ventilating and air conditioning unit, commonly referred to as an HVAC unit. The HVAC unit has a capacity and capability to simultaneously heat and cool different zone areas within the enclosure.

Although functional, the presently known systems, both single zone and multizone, have inefficient energy utilization characteristics. That is, energy use penalties are incurred with operation of the system, as designed.

SUMMARY OF-TI-IE INVENTION In a principal aspect, the present invention is an air processing system for an enclosure having at least two temperature zone areas. The system includes a multizone heating, ventilating and air conditioning unit having a basic energy heat source, an air cooler and appropriate duct work. The air cooler includes an evaporator and heat reclaim condenser. The basic energy heat source and reclaim condenser are situated within the hot deck of the multizone unit.

The multizone heat, ventilating and air conditioning unit also has economizer cycle capability. As used herein, the terms economizer," economizer cycle, and obvious modifications thereof are defined as air conditioning or cooling utilizing outdoor air to the maximum possible extent, with or without mechanical refrigeration.

The system also includes a control mechanism which continuously monitors the temperatures of the zones within the enclosure, power input to the basic energy heat source and enthalpy of the outdoor air drawn into the system. If the power input and outdoor air enthalpy are less than a predetermined power threshold and enthalpy threshold, respectively, the multizone heating, ventilating and air conditioning unit functions, in response to the control mechanism, in the economizer mode. If either condition, i'.e., power and enthalpy is not met, the control mechanism activates the air cooler, whereby mechanical cooling and reclaim heating occurs in the cold and hot deck, respectively, of the multizone unit.

It is thus an object of the present invention to provide an effective and efficient air processing system for a multizone enclosure.

It is another object of the present invention to provide an air processing system utilizing a multizone heating, ventilating and air conditioning unit wherein the operation of the multizone unit and conditionswithin the enclosure are continuously monitored by a control mechanism to determine and effect the most efficient operational mode of the multizone unit.

These and other objects, advantages and features of the present invention will become apparent in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will be described, in detail, with reference to the drawing wherein:

FIG. 1 is a simplified schematic diagram illustrating a preferred embodiment of the present invention;

I FIG. 2 is a detailed schematic diagram of the preferred embodiment shown in FIG. 1 illustrating the structural features with reference to a single zone;

FIG. 3 is a perspective view of an air conditioner or cooler for use in the preferred embodiment shown in FIG. 1;

FIG. 4 is a graph illustrating the temperature-dependent enthalpy threshold of an enthalphy control for use in the preferred embodiment shown in FIG. 1; and

FIG. 5 is a schematic diagram of a control mechanism for use in the preferred embodiment shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention is shown simplistically and schematically in FIG. 1 as an air processing system 10. The system 10 processes and conditions the air in an enclosure 12 having a series of thermal or temperature zones 14, 16, 18. Although three zones 14, 16, 18 are illustrated in FIG. 1, it is to be understood that the system 10 has the capability to serve an enclosure 12 having two or more thermal zones.

As shown, the system 10 is a roof-top system operating in a plenum, generally designated 20. Again this is simply illustrative of a single application of the present invention.

Referring now to FIGS. 1 and 2, the system '10 includes a heating, ventilating and air conditioning unit 22 (hereinafter referred to as the HVAC 22), outdoor air duct 24, return air duct 26, supply air duct 28, thermostat 30 and control mechanism 32. As shown, the outdoor air duct 24 and return air duct 26 deliver quantities of outdoor and indoor air, respectively, to the plenum 20 and l-IVAC 22. The outdoor air passes through an air inlet 34 and is regulated by an outdoor air damper 36 located within the outdoor air duct 24. Similarly, the indoor air passes through air-passing light fixtures 38, or other devices such as grilles, in the zones l4, 16, 18 and is regulated by an indoor air damper 40. The outdoor and indoor air are mixed in an intake region, generally designated 42, to produce a stream of intake air for the l-IVAC 22. The dampers 36, 40 are operated and positioned by the control mechanism 32 through a motor 44.

The outdoor air damper 36 is normally operable in a closed position or state. In this specification, the terms closed, closed position, and closed state" with reference to the outdoor air damper 36 define a minimum set point, as opposed to a truly closed position.

3 That is, at minimum set point, the outdoor air damper 36 permits a predetermined quantity of outdoor air, e.g., to be drawn into plenum 20 for ventilation purposes.

The HVAC 22 includes, from upstream to down-.

stream, an air filter 46, air handler or blower 48 operated by a motor 50, air heater 52 and air cooler or conditioner, generally designated 54. The HVAC 22 also includes an interior partition 56 which physically defines the HVAC 22 into an upper cold deck 58 and a lower hot deck 60. As shown, the air handler 48 operates upon the intake air drawn through the air filter 46 to produce two streams of air, designated by arrows 62, 64. The streams 62, 64 flow within the cold deck 58 and hot deck 60, respectively.

The air heater 52 is a source of basic heat, such as natural gas, direct element electric heat or hot water coils. In this preferred embodiment and for purposes of illustration, a two-stage direct element electric heater 52 is utilized. The air heater 52 is located within the hot deck 60 and directly communicates with the air stream 64.

The air cooler 54 includes an evaporator 66, compressor 68, first or heat reclaim condenser 70 and second condenser 72. As shown, the evaporator 66 is preferably located in the upper, cold deck 58, while the first or heat reclaim coil 70 is within the lower, hot deck 60 of the HVAC 22. The evaporator may, however, interpose the air filter 46 and air handler 48. The condenser 72 communicates directly with the outdoor air for maximum heat rejection at outdoor design conditions.

The air cooler 54 is shown in greater detail in FIG. 3. As shown, the air cooler 54 includes the evaporator 66, a series of compressors 68a, 68b, 686 (shown schematically at 68 in FIG. 2), the first or heat reclaim condenser 70, a series of second condensers 72a, 72b, 720 (shown schematically at 72 in FIG. 2 an accumulator 74, and an expansion valve network 76, interconnected as illustrated, by a series of refrigerant circuit lines, generally designated 78 (not shown for clarity in FIG. 2).

The compressor 68a, or lead compressor, is a twospeed capacity control type, while the remaining compressors 68b, 68c are fixed capacity type. In operation, the compressors 68a, 68b, 68c are cycled on and off, high and low by the control mechanism 32 to provide the necessary refrigeration.

As shown, the expansion valve network 76 interposes the first or heat reclaim coil 70 and the evaporator 66. Regulation of the expansion valve network 76 effectively controls the operational mode of the first or heat reclaim coil 70. That is, if the second condenser 72 and expansion valve network 76 are operating normally, the active quantity of refrigerant in the system is such that only liquid refrigerant leaves the second condenser 72. Therefore, any heat transfer in the first or heat reclaim condenser 70 is a minimum amount equal to the sub-cooling of the liquid refrigerant.

Conversely, to produce maximum heat in the first or heat reclaim condenser 70, the second condenser 72 is de-activated, e.g., by rendering inoperative the condenser fan, generally designated 79 in FIG. 3. Additionally, the expansion valve network 76 effects an accumulation of refrigerant in the accumulator 74. The combined effect of de-activating the second condenser 72 and reducing the active amount of refrigerant in the system causes the principal condensation and resulting 4 heat transfer to occur in the first or heat reclaim condenser 70.

Referring again to FIG. 2, the cold and hot decks 58, 60 of the HVAC 22 extend into the supply air duct 28. The duct 28 directs processed supply air, shown by arrow 80, to the zone 14 of the enclosure 12. For the purpose of clarity, the supply duct work 28 is shown for only zone 14. It is to be understood however, a similar structure exists for each additional zone 16, 18.

As shown, the supply air duct 28 includes a pair of supply air dampers 81, 82. The dampers 81, 82, driven coordinated by a motor 84 responsive to the control mechanism 32, regulate and control the content and temperature of the supply air stream 80. That is, depending upon the temperature conditions of the zone 14, the supply air dampers 81, 82 will adjust to deliver only heated air from the hot deck 60, only cooled air from the cold deck 58, or a mixture thereof.

The system 10 also includes a power sensing or measuring device 86, such as a wattmeter or current sensing relay (hereinafter referred to as power meter 86) having associated switch contacts 87 and an enthalpy monitor or control 88 having switch contacts 89. The switch contacts 87, 89 are shown in FIG. 5. The power meter 86 continuously monitors the input power to the air heater 52 to determine whether the power input exceeds a predetermined power threshold. The switch contacts 87 are normally open and close whenever the input power exceeds the power threshold. The power threshold of the power meter 86, as discussed in detail below, is substantially equal to the power input necessary to operate the air cooler 54. If an alternative heat source 52 is utilized, as discussed above, an alternative power monitoring device 86 must also be used.

Similarly, the enthalpy control 88 continuously monitors the enthalpy of outdoor air drawn through the air inlet 34 to determine whether a predetermined, temperature-dependent enthalpy threshold is exceeded. The normally closed switch contacts 89 open whenever the enthalpy threshold is exceeded.

FIG. 4 illustrates graphically the acceptable range of outdoor air conditions, as determined by the enthalpy control 88. That is, outdoor air having a temperature and humidity within the cross-hatched area of FIG. 4 will have an enthalpy less the temperature-dependent threshold of the enthalpy control 88.

Referring to FIG. 5, the control mechanism 32 includes a logic circuit, shown schematically at 90, transformer 82, first, second and third heating switches 94, 96, 98, cooling switch 100, relay 102 having normally closed contacts 104, relay 106 having normally open contacts 108, relay 110 having normally open contacts 112, relay 116 having normally open contacts 118, relay 120 having normally open contacts 122 and normally closed contacts 123, relay 124 having normally open contacts 126, and a power supply, generally designated 128, connected as shown. The power supply 128 is a conventional 120 volt, 60 hertz source. The transformer 92 reduces the supply voltage to 24 volts AC.

The logic circuit 90 receives heating and cooling demands from the thermostats 30 in the zones 14, 16, 18. In response, the logic circuit 90 continuously matches the temperature of the cold deck 58 and hot deck 60 of the HVAC 22 to the hottest and coldest zone temperatures, respectively. The logic circuit 90 is available from Ranco Controls Division of Columbus, Ohio under the trade name of EA3 Load Analyzer Control Module. Additionally, the Ranco control module is described, in detail, in US. Pat. Nos. 3,788,386 and 3,820,713. The Ranco logic circuit 90 operates under the 24 volts AC provided by the secondary winding of the transformer 92.

More particularly, the thermostat 30, demanding the greatest heating, causes the heating switches 94, 96, 98 to progressively close in response to need. The closing of heating switch 94, indicative of lowest heating demand, energizes the relays 102, 106, opening contacts 104 and closing contacts 108. As a result, the second condenser fan 79 ceases operation and the first or heat reclaim condenser 70 is activated to process the air stream 64, provided the air cooler 54 is operative. If the air cooler 54 is inoperative or additional heating is required, the heating switches 96, 98 progressively close, energizing relays 110, 116, respectively, and thereby activating the first and second stages of air heater 52.

In response to the thermostat 30 demanding the greatest cooling, the control mechanism 32 through motor 44 variably opens the outdoor air damper 36, provided the switch contacts 87, 89 are open and closed, respectively. This is accomplished by imposition of a potential across the command terminals 130 of the logic circuit 90. Additional cooling demands cause cooling switch 100 to close, thereby energizing the air cooler 54. If heating is simultaneously required, the first or heat reclaim condenser 70 and, if necessary, the air heater 52 will be active.

The closing of switch contacts 87 or opening of switch contacts 89 effectively terminates outdoor air cooling, i.e., the economizer cycle. The opening of switch contacts 89 disconnects the motor 44 from the command terminals 130. The closing of switch contacts 87 energizes relay 120, opening contacts 123. In either event, the outdoor air damper 36 is closed.

Further, the closing of switch contacts 87 causes contacts 122 to close, thereby maintaining the relay 120 in an energized state until contacts 108 open. Thus, the outdoor air damper 36 is locked in a closed position until all heating demands are met, i.e., until relay 106 is de-energized by opening of heating contacts 94. Thus, despite the fact that the power threshold of the power meter 86 exceeds the input power to the air heater 52, the system will not return to the economizer cycle until heating requirements are fulfilled. This latching circuitry substantially avoids rapid and excessive cycling of the air cooler 54.

With switch contacts 87 closed or switch contacts 89 open, the cooling switch 100 will close in response to a demand for cooling from a thermostat 30. If heating is also required, the first or heat reclaim condenser 70 will be activated. As such, the system 10 operates in a boot strap heat pump mode until the cooling demand ceases or heat requirement in the air hot deck 60 drops to substantially zero.

As illustrated schematically in FIG. 2, the control mechanism 32 is responsive to the thermostats 30, the power meter 86-and the enthapy control 88 and controls or regulates the HVAC 22, including the air heater 52 and air cooler 54, the outdoor air damper 36,

i the return air damper 40, and the supply air dampers '81, 82. The operational states of the control mechanism 32 are summarized below:

STATE CONDITIONS (c) power threshold exceeds power input In the lst and 2nd states, and under the assumption that a thermostat 30 demands heating, the air cooler 54 is operative, such that the evaporator 66 cools the air stream 62 and the first or heat reclaim condenser 70 heats the air stream 64. Additional heating, if necessary, is provided by the air heater 52, i.e., the air heater 52 cooperates with the first condenser 70 in processing the hot deck air stream 64. In the 3rd state, cooling is effected by use of outdoor air, while heating is effected by the air heater 52 alone.

If there is no heating demand during 1st and 2nd stage operation of control mechanism 32, the second condenser 72 will operate normally, de-activating the first or heat reclaim condenser 70. This substantially avoids the problem of wiping" experienced in the presently known multizone air processing systems. That is, as shown in FIG. 2, air entering the cold deck 58 contacts the surface of the hot deck 60. In the previous systems, this wiping elevated the temperature of the air stream 62, requiring additional cooling in the cold deck 58. in the present invention, the first or heat reclaim condenser 70 is inactive, i.e., de-activated, whenever heating demands are fully satisfied and heating switch 94 is open. Thus, heat transfer is substantially avoided.

As discussed above, the power threshold of the power meter 86 is preferably substantially equivalent to the minimal operational power input of the air cooler 54. Switching from outdoor air cooling to mechanical refrigeration preferably occurs at this power level because mechanical refrigeration provides both cooling and reclaim heating, while reducing heating requirements through utilization of minimum outdoor air.

Utilization of multiple compressors 68, including a two-speed capacity control lead compressor 68a, significantly facilitates tracking of the refrigeration load. Fractional horsepower is also substantially reduced, thereby increasing the relative efficiency of the system 10, as a whole. In addition, location of the evaporator 66 in the cold deck 58 of the HVAC 22 permits the heat from the air handler motor to be treated as machine sensible load.

The significance of the discriminating capability of the system 10, i.e., the ability to effectively choose between outdoor air cooling-mechanical, secondary heating and mechanical cooling-reclaim heating, is theoretically shown in Table I. For each outdoor air temperature, Case No. 1 compares a multi-zone unit utilizing outdoor air for cooling with a multizone unit utilizing refrigeration and heat reclaim in a heatingdominant situation. Case No. 2 presents a similar comparison in a cooling-dominant mode.

Mid-range outdoor air temperatures of 45 to F were analyzed for three basic reasons. First, the presently known systems are, generally speaking, most inef- 7 ficient over this range. Second, in this range, the most diverse internal space temperature requirements occur. And third, the mid-range outdoor air temperatures occur in geographical areas where heating and air conditioning systems are applied.

TABLE I have, in the past, been generally recognized as a superior system. The present invention, however, has the capability to utilize heat rejected by zones requiring cooling in zones requiring heating. This is properly characterized as free heat. By definition, the multi- COMPARATIVE ENERGY (KW) WITH MINIMUM OUTSIDE AIR AND ECONOMIZER CYCLE OUTDOOR AIR HEATING AND ENERGY use of refrigerated cooling in the cold deck 58 and heat reclaim in the hot deck 60 provides the most efficient energy utilization. If, on the other hand, cooling is predominantly required, the economizer cycle is most efficient. The system 10 maximizes efficiency by continuously monitoring the energy used by the hot deck air heater 52 and enthalpy of the outdoor air and selecting the most advantageous mode of operation of the HVAC 22.

By computer simulation, the system 10 has been compared, in terms of energy consumption, to various other systems, including multiple single zone units, with and without economizer cycles, a damperless multizone unit and a drawthrough multizone unit, with and without an economizer cycle. The results are shown in Table 11.

It is readily apparent that the system 10 displayed a performance advantage for each randomly selected test point. Substantial energy savings are, therefore, available with utilization of the system 10.

ple single zone units lack this free heat capability. Additionally, the presently known multiple single zone units do not have heat exchange capability, i.e., an evaporator in the cold deck and and an associated heat reclaim condenser in the hot deck.

It is well known that the damperless multizone unit, which includes an individual basic energy heat source and evaporator for each zone, does not generally include an economizer cycle. Thus, the performance advantage of the present invention with respect to the damperless multizone unit is derived from the capacity to utilize outdoor air, with or without mechanical refrigeration, for cooling. Further, the damperless multizone unit lacks the heat exchange capability discussed above.

In the drawthrough multizone unit, intake air is drawn through the evaporator prior to division into hot and cold deck air streams. In the present invention, however, the evaporator 66 is situated within the cold deck 58 of the HVAC 22, such that only the volume of air necessary for conditioning the zones 14, 16, 18 of the enclosure 12 is mechanically cooled.

A single preferred embodiment of the present invention has been herein disclosed. It is to be understood, however, that various modifications and changes can TABLE II COMPARISON OF POWER INPUT (KW) OF 10,000 CFM SYSTEMS WITH TYPICAL CONDITIONS MULTIPLE SINGLE DAMPER- DRAWTHROUGH LESS ZONE MULTIZONE MULTIZONE OUTDOOR AIR HEATIN COOLIN WITH WITHOUT WITHOUT WITH WITHOUT PRESENT TEMPERA- cfm F cfm F ECONO- ECONO- ECONO- ECONOMIZER ECONO- INVENTION TURE MIZER MIZER MIZER MIZER In analyzing and comparing the tested systems, it should be noted that the multiple single zone units,

be made without departing from the true scope and spirit of the present invention, as defined in the follow- 9 ing claims. I

What is claimed is:

l. A system for processing a volume of indoor air in an enclosure, said enclosure having at least a first and second thermal zone, said indoor air in said first and;

second thermal zone having a first and second zone temperature, respectively, said first zone temperature exceeding said second zone temperature, comprising, in combination:

thermostatic means for sensing said first and second zone temperatures, said thermostatic means having a predetermined cooling threshold and a predetermined heating threshold; multizone air processing means for producing a first stream of cooling supply air having a first stream temperature and a second stream of heating supply air having a second stream temperature, said multizone air processing means including air heating means having a power input and air cooling means including evaporator means, compressor means and first condenser means, said air heating means and said first condenser means communicating directly with said second stream, said thermostatic means regulating said first and second air stream temperatures according to said first and second zone temperatures, respectively;

outdoor air duct means for supplying a first quantity of outdoor air having an enthalpy to said multizone air processing means, said outdoor air duct means including outdoor air damper means for regulating said first quantity;

return air duct means for supplying a second quantity of indoor air to said multizone air processing means, said return air duct means including return air damper means for regulating said second quantity;

first means for monitoring said enthalpy of said outdoor air, said first means having a predetermined enthalpy threshold; I

second means for monitoring said power input to said air heating means, said second means having a predetermined power threshold; and

means for controlling said multizone air processing means, said outdoor air damper means and said return air damper means in response to said thermostatic means, said first means and said second means, said outdoor air duct means and said return air duct means cooperatively defining means for supplying a quantity of intake air to said multizone air processing means, said intake air being a mixture of outdoor and return air and having a predetermined intake temperature, said controlling means being operable in a first state whenever said first zone temperature exceeds said cooling threshold and said enthalpy exceeds said enthalpy threshold, a second state whenever said first zone temperature exceeds said cooling threshold and said power input exceeds said power threshold, and at least a third state whenever said first zone temperature exceeds said cooling threshold, said enthalpy threshold exceeds said enthalpy and said power threshold exceeds said power input, said air cooling means, said outdoor air damper means and said indoor air damper means being operative, closed and open, respectively, in said first state, said air heating means cooperating with said first condenser means in said first state to process said second stream, said air cooling means, said outdoor air damper means and said return air damper means being operative, closed and open, respectively, in said second state, said air heating means cooperating with said condenser means in said second state to process said second stream, said air cooling means, outdoor air damper means, return air damper means and air heating means bieng inoperative, variably open, variably open and operative, respectively, in said third state.

2. A system as claimed in claim 1 wherein said enclosure includes a third zone having a third zone temperature, said third zone temperature interposing said first and second zone temperatures.

3. A system as claimed in claim 1 wherein said controlling means further includes relay means for maintaining said controlling means in said second state whenever said power input drops below said power threshold until said second zone temperature substantially equals said heating threshold substantially avoiding excess cycling of said air cooling means.

4. A system as claimed in claim 1 wherein said evaporating means directly communicates with said first stream in said multizone air processing means.

5. A system as claimed in claim 1 wherein said air cooling means has a minimum operational power input.

6. A system as claimed in claim 5 wherein said minimum operational power input and said power threshold are substantially equal.

7. A system as claimed in claim 1 wherein said air cooling means includes a second condenser means and expansion valve means interposing said first and second condenser means, said second condenser means and said expansion valve means cooperating to define means for de-activating said first condenser means.

8. A system as claimed in claim 7 wherein said controlling means is operable in a fourth state whenever said air cooling means is operative and said second zone temperature exceeds said heating threshold and a fifith state whenever said air cooling means is operable and said heating threshold exceeds said second zone temperature, said de-activating means being operative and inoperative, respectively, in said fourth and fifth states.

9. A system as claimed in claim 7 wherein said multizone air processing means includes supply air duct means for directing said first and second streams to said first and second zones, respectively.

10. A system as claimed in claim 9 wherein said supply air duct means further includes supply air damper means for mixing said first and second streams to produce a third stream of supply air, said supply air duct means directing said third stream to said third zone. 

1. A system for processing a volume of indoor air in an enclosure, said enclosure having at least a first and second thermal zone, said indoor air in said first and second thermal zone having a first and second zone temperature, respectively, said first zone temperature exceeding said second zone temperature, comprising, in combination: thermostatic means for sensing said first and second zone temperatures, said thermostatic means having a predetermined cooling threshold and a predetermined heating threshold; multizone air processing means for producing a first stream of cooling supply air having a first stream temperature and a second stream of heating supply air having a second stream temperature, said multizone air processing means including air heating means having a power input and air cooling means including evaporator means, compressor means and first condenser means, said air heating means and said first condenser means communicating directly with said second stream, said thermostatic means regulating said first and second air stream temperatures according to said first and second zone temperatures, respectively; outdoor air duct means for supplying a first quantity of outdoor air having an enthalpy to said multizone air processing means, said outdoor air duct means including outdoor air damper means for regulating said first quantity; return air duct means for supplying A second quantity of indoor air to said multizone air processing means, said return air duct means including return air damper means for regulating said second quantity; first means for monitoring said enthalpy of said outdoor air, said first means having a predetermined enthalpy threshold; second means for monitoring said power input to said air heating means, said second means having a predetermined power threshold; and means for controlling said multizone air processing means, said outdoor air damper means and said return air damper means in response to said thermostatic means, said first means and said second means, said outdoor air duct means and said return air duct means cooperatively defining means for supplying a quantity of intake air to said multizone air processing means, said intake air being a mixture of outdoor and return air and having a predetermined intake temperature, said controlling means being operable in a first state whenever said first zone temperature exceeds said cooling threshold and said enthalpy exceeds said enthalpy threshold, a second state whenever said first zone temperature exceeds said cooling threshold and said power input exceeds said power threshold, and at least a third state whenever said first zone temperature exceeds said cooling threshold, said enthalpy threshold exceeds said enthalpy and said power threshold exceeds said power input, said air cooling means, said outdoor air damper means and said indoor air damper means being operative, closed and open, respectively, in said first state, said air heating means cooperating with said first condenser means in said first state to process said second stream, said air cooling means, said outdoor air damper means and said return air damper means being operative, closed and open, respectively, in said second state, said air heating means cooperating with said condenser means in said second state to process said second stream, said air cooling means, outdoor air damper means, return air damper means and air heating means bieng inoperative, variably open, variably open and operative, respectively, in said third state.
 2. A system as claimed in claim 1 wherein said enclosure includes a third zone having a third zone temperature, said third zone temperature interposing said first and second zone temperatures.
 3. A system as claimed in claim 1 wherein said controlling means further includes relay means for maintaining said controlling means in said second state whenever said power input drops below said power threshold until said second zone temperature substantially equals said heating threshold substantially avoiding excess cycling of said air cooling means.
 4. A system as claimed in claim 1 wherein said evaporating means directly communicates with said first stream in said multizone air processing means.
 5. A system as claimed in claim 1 wherein said air cooling means has a minimum operational power input.
 6. A system as claimed in claim 5 wherein said minimum operational power input and said power threshold are substantially equal.
 7. A system as claimed in claim 1 wherein said air cooling means includes a second condenser means and expansion valve means interposing said first and second condenser means, said second condenser means and said expansion valve means cooperating to define means for de-activating said first condenser means.
 8. A system as claimed in claim 7 wherein said controlling means is operable in a fourth state whenever said air cooling means is operative and said second zone temperature exceeds said heating threshold and a fifith state whenever said air cooling means is operable and said heating threshold exceeds said second zone temperature, said de-activating means being operative and inoperative, respectively, in said fourth and fifth states.
 9. A system as claimed in claim 7 wherein said multizone air processing means includes supply air duct means for directing said first and second streams to said first and second Zones, respectively.
 10. A system as claimed in claim 9 wherein said supply air duct means further includes supply air damper means for mixing said first and second streams to produce a third stream of supply air, said supply air duct means directing said third stream to said third zone. 